New coalition talks

The coalition that Mr Borisov formed upon re-election in 2014 relies on the support of centre-left and nationalist parties.

Outgoing President Rosen Plevneliev is expected to chair negotiations to form a caretaker government, but early elections are expected as soon as March.

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President-elect Radev says good ties with Russia and the EU are not incompatible

Mr Radev, 53, launched his presidential bid as an independent candidate, supported by a group of citizens, and only later got Socialist Party (BSP) backing. He will be sworn in as president in January.

He reached out to nationalists by opposing the EU's resettlement policy for refugees. That policy is also rejected by some other ex-communist EU member states in Eastern and Central Europe.

Mr Radev spent 27 years rising through the ranks of the Bulgarian air force. He also received training at the US Air War College in Alabama. Bulgaria joined Nato in 2004, along with other ex-Soviet bloc countries.

"Until recently, I flew a Soviet jet fighter. I graduated from a US academy. But I am a Bulgarian general. My cause is Bulgaria," he said.